Käthe Petersen sits alone on the stage. She’s a well-read woman; a nurse, a social worker, honoured by post-war West Germany for her compassion and charity. But she was also a Nazi, who sent thousands of women to modern-day workhouses for nothing more than having sex with the wrong man. That dichotomy – the two faces of her character – is the riddle of Taboo, a disturbing one-woman play that shines a light on an under-appreciated aspect of European history.

Actor-playwright Karin Schmid plays Petersen, while her victims are represented by recorded voiceovers that play through a vintage radio. At times, Petersen’s attitudes seem grimly comical: she shows us a checklist of modern societal problems, which include women’s ‘New Independence’ and, horror of horrors, ‘Having a Job’. But these laughable opinions had deadly consequences, and we learn how she became a collective legal guardian for hundreds of women, using her power to frustrate even Nazi-era courts which sought to protect those she accused.

Much of the chill flows from the disconnect between Petersen’s worldview and ours; her willingness not just to defend, but even to celebrate, techniques we find inhuman today. As she listens to the testimonies, Schmid maintains a severe and controlled demeanour; she nods in acknowledgement of the facts we hear, but is seemingly untouched by the human outcomes. Caring, to her, means ‘protecting’ society, which in turn implies control over female sexuality. Petersen speaks with pride of the system she’s created, yet her self-congratulation stands in sharp contrast to the evidence we hear played.

But this justified focus on the victims’ stories does, to a degree, undercut the show’s central theme. It’s called Taboo because (as the script puts it) this story ‘sails under the radar of our collective consciousness’: incredibly, Petersen’s misdeeds were overlooked after the War, and her work was honoured by the city of Frankfurt as late as 1978. Although Schmid highlights this fact, she never really asks how it happened, or what it tells us about post-War attitudes in Germany and beyond. The programme notes draw an interesting parallel with the notorious Magdalene Laundries that existed across Europe – but based on the show alone, it would be all too easy to view Peterson as a Nazi aberration, in the same mould as Eichmann or Mengele.

And perhaps because this founding concept remains relatively unexplored, the play’s structure is a little unwieldy. We’re told that we’re the audience for a provocative chat show, and Schmid first appears as its host to outline the concept of ‘Taboo’. But that comes at the cost of an awkward pause, as she changes costume backstage to become Petersen; and the chat-show format is from then on reduced to a series of questions played as voiceover. Maybe this concept warrants a re-think, or perhaps Schmid would prefer to double down on it – there’s a post-performance audience Q&A which could quite easily be re-imagined as an integral part of the show.

A couple of high-concept mask sequences jar a little, set as they are the naturalistic tone of the rest of the play, but the vintage advertisements that accompany them are themselves a reminder of how society’s attitudes inform the way we behave. So there’s a lot of important material packed into Taboo, and the story it tells is one we should know. Stylistically it could be a little clearer and sharper – but intellectually it’s convincing, and dark.